1. Field of Invention
The invention relates to a printing press comprising a plurality of inking systems, which cooperate with at least one impression cylinder.
2. Description of the Prior Art
Such printing presses are primarily known for printing flexible materials. The at least one impression cylinder is often in the form of a single central impression cylinder with which the inking systems cooperate. In place of a single impression cylinder, it is also possible to provide a plurality of impression cylinders that are then arranged such that the web of printing substrate is guided only from one side. For example, the path of the web can closely imitate a circular path.
A printing press comprising a central impression cylinder is usually used for printing plastic webs for packaging purposes. But also webs of paper or paperboard that can be used subsequently for the production of cardboard packaging are often printed by means of these printing presses.
An inking system, which cooperates with an impression cylinder or the impression cylinder, comprises a print roller carrying the actual print image and at least one ink-transfer roller. An inking system of a flexographic printing press usually used for the package printing mentioned above comprises a print roller and a so-called anilox roller in the form of an ink-transfer roller that draws printing ink from an ink reservoir and applies the same to the print roller. The print roller transfers the ink that is applied to only the raised printing plates of the print roller that represent the print image onto the printing substrate. The ink reservoir is mostly an ink chamber blade that together with the anilox roller delimits a closed space.
Primarily in the field of package printing, it is frequently necessary to change not only the print motif but also the print format. Central cylinder flexographic printing presses are therefore constructed such that they exhibit a wide range of variety in formats. For changing the print format, it is usually necessary to change the diameter of at least the print roller.
Two concepts that aim at facilitating these change processes have taken hold in recent years. One concept is formed by the so-called sleeve machines, in which the print and anilox rollers comprise a cylinder mandrel and one or more sleeves that are disposed concentrically thereto. For adapting the format and/or motif, the cylinder mandrels within the inking system can now be exposed at one end thereof so that the sleeves can be pulled off in the axial direction from this end of the cylinder mandrel and new sleeves can be slid onto the rollers. Since the sleeves have relatively low dead weight, they can often be changed manually. The outer sleeve carries the printing plate. Intermediate or adapter sleeves are used for adapting the diameter of the print roller over wide regions. Such a printing press is disclosed in the patent application EP 0 741 009 B1.
A second concept consists in lifting print rollers that are mounted by means of their journals in bearing blocks of the inking systems in their entirety out of the printing press and replacing them with print rollers having different diameters. The print rollers lifted out of the printing press are then usually removed from the printing press by means of suitable transporting carriages and put in storage or set up for the next print job in that the old printing plates are removed and new printing plates are glued onto the outer circumference of the roller. Here, too, sleeves carrying the printing plates can also be fitted on the rollers. Printing presses constructed according to this concept usually ensure improved print quality as compared to printing presses based on the first concept since, in most cases, there is no requirement of adapter sleeves for adapting the diameters of the rollers. The process of adapting the diameters of the rollers is carried out by selecting a base roller having the corresponding diameter. Print rollers comprising adapter sleeves are often susceptible to vibrations. Printing presses constructed according to the second concept are therefore recommended for large printing widths. These printing presses are also referred to as web fed presses.
In the recent past, there has been a strong tendency among orders for operators of printing presses to have smaller batch sizes. It is therefore increasingly important to keep short the unproductive period of time taken to change the motif and format. Printing presses operating according to the first concept are clearly advantageous in this respect particularly when the sleeves can be directly advanced to the inking system in question by means of auxiliary devices such as lifting platforms.
Also in the case of printing presses that ensure high print quality, there is an ever increasing desire to achieve short change times. EP 1016 522 A 1 therefore suggests roller-bearing devices, in the roller-bearing positions of which the print rollers can be mounted so as to be fully prepared for the subsequent print job. The rollers that have already been set up for the follow-up job in a corresponding section of the print operation have to be supplied by a roller-transporting carriage to the roller-bearing device. A robot then places the prepared rollers in the roller-bearing device. After the completion of the current print job, the old rollers and also the doctor blade chambers are first lifted out of each inking system by means of the robot, deposited in the roller-bearing device, and new rollers and a new doctor blade chamber are removed from the roller-bearing device and conveyed to the inking system. When the process of changing the rollers is complete, the old rollers can be loaded onto the transporting carriage and removed, and then new rollers are again supplied by the transporting carriages to the roller-bearing device.
Yet, the process of repeatedly loading up the roller-bearing device takes up too much time particularly since printing presses these days can often process more than 600 meters of printing substrate per minute. The print rollers are often not available for the subsequent job when the current print job is complete.